LPR (License Plate Recognition) or ALPR (Automatic License Plate Recognition) is an object recognition technology that typically includes image-processing operations with functions as the core module of “intelligent” transportation infrastructure applications. License plate recognition techniques, such as ALPR, can be employed to identify a vehicle by automatically reading a license plate utilizing image processing and character recognition technologies. A license plate recognition operation can be performed by locating a license plate in an image, segmenting the characters in the captured image of the plate, and then performing an OCR (Optical Character Recognition) operation with respect to the identified characters.
The ALPR problem is often decomposed into a sequence of image processing operations: locating the sub-image containing the license plate (i.e., plate localization), extracting images of individual characters (i.e., segmentation), and performing optical character recognition (OCR) on these character images.
A problem in license plate recognition technologies that must be considered is the presence of color. Consider a license plate with a colored pictorial background. Eventually, it is desirable to present a binary image to an OCR module. The simple technique of rendering a gray image from luminance channel of the colored image, then thresholding it, often confuses pictorial elements of the image with the characters.